The present invention relates to electrical and electronic displays and, more particularly, to a type of display in which a display zone is scanned repeatedly by one or more arrays of lights to create the illusion of an image floating in space.
Displays of this type are known. Illustrative examples include those described by Lock in UK Patent Application No. GB 2 093 617 A and by Belcher et al. in U.S. Pat. No. 5,302,965, both of which are incorporated by reference for all purposes as if fully set forth herein. Generally, these displays consist of a mobile, typically rotating, unit and a stationary unit. For example, in the displays of Lock and Belcher et al., the mobile unit in fact does only rotate with respect to the stationary unit. The mobile unit includes at least one array of light sources, typically light emitting diodes, oriented perpendicularly to the direction of motion of the mobile unit. As the mobile unit moves, the arrays of light sources sweep a path in a display zone. At each of several positions of the arrays within the display zone, different combinations of the light sources are illuminated. This creates the illusion of an image floating in space, with each light source at each position corresponding to one pixel of the image, and one column of pixels being displayed at each position. With appropriate sequencing of the illumination and extinction of the light sources, this image can be animated.
Displays of this kind suffer from two limitations. The first limitation relates to the accuracy with which the light sources can be positioned relative to the desired column positions. In known devices, the positions of the arrays are determined by measuring the position of the mobile unit as a whole, and inferring the positions of the arrays from this single measurement. For example, in one embodiment of Lock's display, the periphery of a slotted disk fixed to the stationary unit is scanned by an optical reading device fixed to the rotating unit to measure the angular position of the rotating unit relative to the stationary unit. The accuracy and stability of the inferred (nominal) positions of the arrays relative to their actual positions then depends on the accurate alignment and mechanical stability of the mobile unit. In principle, only one array needs be used to scan the display zone. In practice, there is a tradeoff between number of arrays, scan speed, and illumination level; and several arrays are needed to achieve an adequate level of illumination and an adequate scan speed. Small inaccuracies in the alignment of the mobile unit, and mechanical instability of the mobile unit, cause the arrays to be in positions other than their nominal positions as the mobile unit move. Because the light sources of the arrays are turned on and off sequentially as though the arrays were in their nominal positions, the resulting image is blurred.
A second limitation of these kinds of arrays relates to the limited amount of data that can be stored on the mobile unit. Typically, the mobile unit stores only as much data as is needed to display a small number of images, with a much larger store of data being stored in the stationary unit. In the display of Belcher et al., for example, data for new images may be transmitted from the stationary unit to the mobile unit, but only at a rate much slower than the rate at which the corresponding signals must be transmitted to the moving arrays. This limits the extent to which these displays may be used to display animated images.
There is thus a widely recognized need for, and it would be highly advantageous to have, a display, of the type in which a display zone is scanned repeatedly by one or more arrays of lights to create the illusion of an image floating in space, in which control signals are transmitted to the arrays according to their actual positions, rather than their nominal positions, and at a rate fast enough to support animation of the floating image.